When you come back from your first day teaching in jail and realize—after taking the train to the bus to the compound, going through three layers of security, speaking with five inmate-students in the chapel for two hours about their lives and Malcolm X and Sherman Alexie and writing and sadness and frustration and hope, boarding the bus and the train back to your apartment—that your knee, a source of near-constant pain for almost a year, hasn’t bothered you all day. You remember this because, as you sit down at your computer to write for the first time in weeks, it has started hurting again.